On 20 August 1942, Thierack assumed the office of Reich Minister of Justice. He introduced the monthly Richterbriefe in October 1942, in which were presented model – from the Nazi leaders' standpoint – decisions, with names left out, upon which German jurisprudence was to be based. He also introduced the so-called Vorschauen and Nachschauen ("previews" and "inspections"). After this, the higher state court presidents, in proceedings of public interest, had at least every fortnight to discuss with the public prosecutor's office and the State Court president – who had to pass this on the responsible criminal courts – how a case was to be judged before the court's decision.
Thierack not only made penal prosecution of all unpopular persons and groups harsher. "Antisocial" convicts on the whole were much more often turned over to the SS. This usually meant Jews, Poles, Russians, and Gypsies. Soon afterwards, though, he utterly forwent any pretense of legality and simply began handing these people over to the SS. Thierack came to an understanding with Heinrich Himmler that certain categories of prisoners were to be, to use their words, "annihilated through work". Ever since coming to office as Reich Minister of Justice in August 1942, Thierack had seen to it that the lengthy paperwork involved in clemency proceedings for those sentenced to death was greatly shortened.
At Thierack's instigation, the execution shed at Plötzensee Prison in Berlin was outfitted with eight iron hooks in December 1942 so that several people could be put to death at once, by hanging (there had already been a guillotine there for quite a while). The mass executions began on 7 September 1943 but due to their rapidity some prisoners were hanged "by mistake". Thierack dismissed these as errors and demanded that the hangings continue.
After the war he was arrested for trial but he committed suicide and escaped trial at nuremberg